Impact of High Penetration of PV Systems on Fault Current Levels in Conventional Distribution System

Abstract

World is facing a major problem of energy crises and pollution. Renewable energy resources are practical solution and alternative to fossil fuel to make the future pollution free. Photovoltaic (PV) as distributed generation is a practical solution to renewable energy resources. However as PV integration is increasing, it is predicted that it has effects on conventional distribution systems. PV-system as distributed generation has multiple effects on voltage profile, line losses, harmonics, power network operation and fault current level. One of the effect is that fault current level can shift which can effect the existing system fault protection equipment and overall infrastructure of distribution system. There are two opinions, regarding to this effect of change in fault current level due to PV penetration. One opinion states that as PV penetration increases fault current level will increase which has negative effect on the fault protection equipment and overall infrastructure. The reason behind increase in fault current level by integration of PV systems with conventional distribution grid is that, total power of the grid’s fault is increased when new sources of power like PV systems are added to the grid and these sources are near to the fault location due to this fault current level can increase. The other opinion states that the change in fault current level will be insignificant with PV penetration. In proposed thesis, it is investigated that which of the above mentioned two opinions is correct. Fault current analysis is performed for two models of (500 kVA and 1 MVA ) grid without and with PV system, for different PV penetration levels. It was investigated by comparing results for grid without and with PV system, where two three-phase (LLLG) faults were generated independently in distribution networks. There is an insignificant change in fault current levels for both 500 kVA and 1 MVA systems. The reason behind no effect of PV penetration on fault current levels is that grid tied inverters are capable of fast disconnection (i.e., in less than four cycles); interrupts the inverter current contribution immediately during a fault event. As response time of inverters is in milliseconds so inverter is able to instantly cease operation after a disturbance is detected. Therefore, the duration of the fault current contributions is also limited. It is typically assumed that the total fault contribution for viii a PV inverter is less than twice the inverters rated output current. Results shows that high penetration of PV system with conventional distribution system is not problematic with respect to fault current levels in distribution systems.